GECOS

General Comprehensive Operating System (GCOS, /ˈdʒiːkoʊs/) is a family of operating systems oriented toward mainframe computers.

The original version of GCOS was developed by General Electric from 1962; originally called GECOS (the General Electric Comprehensive Operating Supervisor). The operating system is still used today in its most recent versions (GCOS 7 and GCOS 8) on servers and mainframes produced by Groupe Bull, primarily through emulation, to provide continuity with legacy mainframe environments. Note that GCOS 7 and GCOS 8 are separate branches of the operating system and continue to be developed alongside each other.

GCOS is a multithreading, multiprogramming operating system originally oriented towards batch processing, although later versions incorporated enhancements for timesharing and online transaction processing environments. Systems running GCOS today use it mainly for batch and OLTP, or as a backend enterprise server.

Although GCOS has a basic architecture similar to that of the IBM 360 and earlier IBM 7090 Series, which was abandoned by IBM for the 360, and subsequent operating systems with which it competed, it was also heavily influenced by projects such as MEDINET, Multics, and WWMCCS, and has inherited a strong security structure in consequence. Hardware and software features combine to render the operating system unusually secure for an operating system of its generation and class. Multics influenced the design of the hardware, with gate-oriented secure transfer-of-control instructions and a hardware-enforced system of security levels very similar to that of the famous Multics rings. Operational environments such as WWMCCS drove development of special security features to allow secure hosting of classified information and compartmentalization. For a time separate versions of the GCOS system with special security features turned on were maintained specifically for government customers.

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